Radio receiving and indicating system



av. 15, 1949 w. A. MILLER 2,488,022

RADIO RECEIVING AND INDICATING SYSTEM Filed Feb. 1, 1945 '7'She'ets-Sheet 1 RA Pl 0 WARN/N 6 BE ICON exp/0 TERM/N66 5mm (WHEELSnow/v) 77 W V n PROPl-k LANDING C ALTITUDE WHEEL ca/vmcr A FOE PLANEBEAM W/I'l-l F/ELD l rzqA/sM/rrma J l M J 2 4 5 0 T 5ND 0F RUNWA rAPPROX. eou/vps a- I I AIR-FIELD I TELEV/S/U/V TVPE SUPER/1E7: REC- WITH,4. c". a: V/DEO AMR Ram r/A/c; JOINT E. F INPUT FDR KEC.

INVENTOR.

MAL/AM A Manse BY 154 4m ATTOR/Vfy Nov. 15, 3949 w. A. MILLER 2,483,022

RADIO RECEIVING AND INDICATING SYSTEM Filed Feb. 1, 1945 7 Sheets-Sheet2 TELEV/S/O/V TYPE SUPER/IET RFC.

WITH 4.05.61 a VIDEO AMP.

700 HIGH AND 700 700 LOW AND TOO F742 70 rHER/GHZ' 174R 70 THELEFF T00HIGH AND T00 T00 LOW AND 700 ON (OI/K51 m? 7'0 THE RIGHT 54/? 70 77/5L677."

INVENTOR. MAL/AM ,4. /I be A TTORNC Y Nov. 15, 1949 w. A. MILLER2,488,022

RADIO RECEIVING AND INDICATING SYSTEM Filed Feb. 1, 1945 '7 Sheets-Sheet3 kbmkbmv mm 95% .3 w%

Nov. 15, 1949 w. A. MILLER RADIO RECEIVING AND INDICATING SYSTEM 7Sheets-Sheet 5 Filed Feb. 1, 1945 hum Q Fl! llllllllllllllll II I *N QWN INVENTOR. l V/u/AM A Mar/e Nov. 15, 1949 w. A. MILLER RADIO RECEIVINGAND INDICATING SYSTEM '7 Sheets-Sheet 6 Filed Feb. 1, 1945 INVENTOR. lV/u/AM /4./1///LL/2 A TTORNEV Nov. 15, 1949 w. A. MILLER RADIO RECEIVINGAND INDICATING SYSTEM 7 Sheets-Sheet '7 Filed Feb. 1, 1945 I] NJINVENTOR. MAL/AM A. M74 L52 Patented Nov. 15, 1949 RADIO RECEIVING ANDINDICATING SYSTEM William A. Miller, Port Jefferson, N. Y., assignmtoRadio Corporation of America, a corporation of Delaware ApplicationFebruary 1, 1945, Serial No. 575,630

I 10 Claims. (Cl. 343-118) 1 This invention relates broadly to the fieldof direction finding, and more particularly to a sys- 'tem for enablingthe operator of a moving vehicle,

such as an aircraft, to quickly determine his posi tion relative to aremotely located radio transmitter. One specific application of theinvention is a blind landing system for aircraft in which the pilot caneasily follow a radio beam having a pattern corresponding to the glidepath for landing the aircraft safely.

An object of the present invention is to provide the pilot of anaircraft with a radio receiving system which furnishes a simple andefficient visual indication on a cathode ray tube of his positionrelative to the axis of a radio beam emitted from a remote radiotransmitter.

Another object is to provide direction finding radio receiving apparatusemploying a lobe switching or conical scanning antenna coupled to atelevision type of receiver whose video output appears on a cathode rayoscilloscope, for use in determining the position of the radio receivingapparatus relative to a remotely located radio transmitter.

Other objects and the features of the invention will appear from areading of the following description in conjunction with drawings,where- Fig. 1 illustrates an airfield equipped with suitable radiotransmitting apparatus, which can be used with the receiver of theinvention located on an aircraft, for enabling the pilot to land safelyby following the radio beam (sometimes referred to as a blind-landingbeam) Figs. 2 and 2a schematically show two circuit embodiments of radioreceiving equipment which can be used on an aircraft in connection witha blind-landing system, or for general direction finding purposes;

Figs. 3a. 3b. and 3c illustrate the visual markoscilloscope of Fig. 2for different positions of the aircraft relative to the axis of theradio beam radiated from the remote transmitter;

Figs. 4a, 4b and 4c illustrate other possible visual markings on thefluorescent screen of the oscilloscope of the receiving system fordifferent positions of the aircraft relative to a remote radiotransmitter when the system of Fig. 2 is employed without the use ofintensification pulses;

Fig. 5 schematically shows another circuit embodiment of radio receivingequipment in accordance with the invention, employing a moreconventional cathode ray tube indicator than ings on the fluorescentscreen of the cathode ray 2 that used in Fig. 2, and a diiferent kind ofswitching arrangement; v

Figs. 6a, 6b and 6c illustrate thevlsual markings on the fluorescentscreen of the cathode ray oscilloscope of the receiving system of Fig. 5for different positions of the aircraft relative to the axis of theradio beam radiated from the remote radio transmitter; Figs. 7 and 8schematically illustrate two other radio receiving circuit embodimentsof the invention, especially adapted for use either with incomingunmodulated continuous waves or modulated continuous waves;

Figs. 9 and 10 schematically illustrate two different electronicswitching circuits which can be used in the receivingsystems of theinvention in place of the mechanical switches; and

Fig. 11 graphically illustrates the operation of the electron switchingsystem of Fig. 10.

Referring to Fig. 1 of the drawing, there is shown an airfield equippedwith a blind-landing radio transmitter system with which the presentinvention may be used. At this field, there is provided a. radiotransmitter at point A for transmitting pulses of ultra short waveenergy toward B, along a runway suitable for the landing of aircraft.The pattern or lobe of the radiated beam is designated C. The axis ofthe cone of radiation C corresponds to the glide path which would landan airplane safely. Suitable radio marking beacons radiating verticalbeams are located at points D and E in such positions relative to theairfield that the pilot is given sumcient warning of his approach to thefield in order for him to attain the proper altitude before entering theblind landing area. It is preferred that the transmitter radiate ultrashort wave energy in order to enable the use of a small compactreceiving antenna on the aircraft; although longer waves can be used atthe transmitter with a correspondingly larger antenna at the receivingequipment in the aircraft.

Fig. 2 shows the radio receiving and visual indicating apparatus whichis placed in the plane for enabling the pilot to determine his positionrelative to the axis of the beam C and to land his aircraft safely. Thereceiving antenna and the reflector are designated respectively I and 2,and are located in the nose of the airship. The mean axis of thereflector (which by way of example may be a paraboloid) and antenna willcorrtespond to the longitudinal axis of the aircraf The antenna I is anyoff-axis rotating element, such as a dipole, driven by a motor 3 whichin combination with the reflector provides a receiving antenna patternor lobe switching system such as described in my copending applicationsSerial Nos. 501,050, filed September 3, 1943, now Patent No. 2,470,939,issued May 24, 1949, and 532,929, filed April 27, 1944. Such a lobeswitch ing system involves causing the receiving antenna pattern tosequentially change direction uniformly over the four quadrants of acircle; that is, the direction of maximum effectiveness of the receivingantenna pattern sweeps through acone whose apex is at the receivingantenna. This is done by spinning the antenna I positioned 01! thecenter or axis of the reflector 2, or by spinning a defleeting elementoff the focus cf the reflector. If a spinning element is employed, itmay be rotated around one end as an axis or, preferably the entireradiator element I is rotated around a circle without changing itspolarization, a process termed nutation. The antenna i thus travels in acircle in the focal plane of the paraboloid. The receiving antennasystem, it will be seen, scans a cone of revolution in the space aheadof the aircraft. The directions of the receiving antenna lobe patternsare, of course, diiferent for difierent quadrants of the circle as theantenna I rotates, and these patterns are made to intersect at thoseplaces where the slopes are greatest, thus providing -maximumsensitivity. These lobes are efiective sequentially; that is, one at atime, and would overlap if they were effective simultaneously.

In the practice of the invention, the speed of rotation of element I ismade to be small compared to the pulse rate of the transmitted energy;ior example, antenna i may be driven at a rate of ten revolutions persecond while the pulse rate of the remote transmitter may be 1000 persecond.

Receiving antenna i is driven by a direct current motor 3 over ametallic shaft 4. This driving motor also turns a small two-phasegenerator 5 over the same metallic shaft, and this generator .5 suppliesvoltages in phase quadrature to the vertical deflection plates V and thehorizontal deflection plates H of a cathode ray oscilloscope tube I2.The motor 3, by means of a metallic shaft, also drives a rotating switchin the form of a rotating insulating drum 6 having four metallicsegments 50 embedded in its periphery and spaced ninety mechanicaldegrees apart. These metallic segments 50 are directly connectedtogether by a metallic band I and are connected to a source of positivedirect current potential +E through a brush 1 and a resistor 8. A brush9 engages the periphery of the drum 6 and supplies a positiveintensifier pulse to the control grid in of the oscilloscope I2 overlead Il each time the-brush contacts one of the segments 50. CondenserI6 is a blocking condenser which isolates the control grid I0 from thenegative source HV and from ground. The metallic shaft which drives thedrum 6 is connected to a rotating joint I3 as a result of which theshaft to the left of joint I3 can rotate while the metallic shaft to theright of joint I3 is stationary. It will thus be seen that the'metallicshafts form a radio frequency transmission line from antenna I, throughelements 3, 5, 6 and I3, to the receiver I4.

It should be understood that the mechanical arrangement of directcurrent motor, two-phase generator and rotating switch 6 is only aspecial embodiment, and that other variations of these elements arepossible. For example, if alternating current is available in theaircraft, then direct current motor 3 can be replaced by a synequipment.

chronous motor, while the two-phase generator can be replaced by a phasesplitting circuit to provide a circular sweep for the oscilloscope. Ican thus use either .mechanical or electrical phasing The rotatingswitch 8 can be replaced by an electronic switching scheme along thelines described in my copendlng application. Serial No. 532,929,supraQin order to provide intensifier pulses. Suitable electronicswitchers to replace the mechanical switch 6 are described hereafter inconnection with Figs. 9 and 10.

Cathode ray tube I2 is constructed in such manner, and has its deflectedplates V and H provided with voltages in phase quadrature, that theelectron beam which would normally be seen on the screen S traverses acircle. This tube I2 is provided with a control grid I0, a focussingelectrode I1 and a second anode I8. A subsidiary electrode I5 on theoscilloscope is provided to which the radial deflecting voltage isapplied from the output of the receiving system I4 over lead I5. Such anoscilloscope is available and known in the art. The electron beam spoton the screen of the oscilloscope is arranged to traverse a circularpath in synchronism and in a 1:1 relation with the antenna loberotation. This means that the spot should travel once over the circle onthe screen S each time the receiving antenna patterns or lobes areswitched through all four consecutive quadrants. The intensifier pulsesupplied to the control grid I0 from the rotating switch is ofsuflicient magnitude to overcome the cut-oif bias normally applied tothis grid and render the cathode ray beam visible on the screen. It willbe noted that in the absence of an intensifier pulse applied to thecontrol grid ill, the electron beam in the oscilloscope will not reachthe screen S.

The receiver I4 is a television type ofsuperheterodyne receiver and hasa wide intermediate frequency band width, wide band detector, anautomatic gain control (A. G. C.) circuit of this television type ofreceiver, and provides a video output for lead I5. The gain of thereceiver I4 is controlled. by the particular incomin signal havingmaximum amplitude. This gain control is not necessary since manualcontrol could be used, but the automatic feature is desirable from anoperational standpoint. Some control is necessary, however, since thereceiver cannot be allowed to saturate because this system depends forits operation upon matching the amplitudes on the oscilloscope, ofsignals delivered by the receiyer to the oscilloscope when the receivingantenna is in various positions. By the term saturate, I mean that thepulse in the preceding part of the receiver should not have such a largeamplitude as to drive a succeeding stage appreciably beyond the linearportion of the operating characteristic curve; for example, the gridvoltageplate current characteristic. This may also be avoided byamplified back-bias; a system which provides very little loss in gainfor signals of low amplitude but great loss in gain for signals of largeamplitude. The video output of the receiver need not have as wide afrequency range as the television receiver but may for example be aswide as 2000 kilocycles (2 megacycles). Receiver it, however, requiresno synchronization circuit such as is present in the conventionaltelevision receiver. The duration of the pulses radiated by the remotetransmitter (assuming ultra high frequency energy is employed), and therate at which these pulses build up determine the necessary band widthin the video circuit in the receiver ll. For example, the transmittermay send out pulses of one-microsecond duration in which case the videocircuit band width of the receiver ll should not be less than onemegacycle. If, for

and intermediate frequency pass band to accommodate any possiblefrequency deviation of the transmitter. in the assumed case 30megacycles. The video portion of the receiver it. however, is controlledonly by the width and build up time of V the received pulse passed on toit by the second detector, and hence the band width of this videocircuit need only be 1 to 3 megacycles wide.

A brief description of the operation of the receiving system of Fig. 2will now be given: Assuming that pulses are radiated from the remotetransmitter located at A in Fig. 1 at a rate of 1000 per second, andthat the receivin antenna rotates at 10 revolutions per second, andfurther that the switch segments 50 on drum 6 are each nine mechanicaldegrees wide, it will be evident that there are received in the systemof Fig. 2 two and one-half pulses during the passage of the brush 9 overeach segment. The width of the segments 50 is a matter of choice. Eachtime the switch 6 supplies a positive intensification pulse to the gridHi, there will be supplied two and one-half video pulses to the radialdeflecting electrode 65. The intensification pulse will permit theelectron beam to pass through it to the screen S of the tube I! whilethe simultaneously occurring radial deflecting pulses on electrode lserve to pull the electron beam toward the center of the screen S andproduce a line on the screen similar to that shown in Figs. 3a, 3b and3c. The circular lines on the screen are en raved on transparentmaterial placed over the face of the screen to facilitate comparing ormatching of the dimensions of the radial beam lines appearing on thescreen. Since the intensification pulses occur four times per revolutioncorresponding to the four lobe positions, there will be four radiallines on the screen. Due to the repeated occurrence of these pulses andthe phenomenon known as the persistence of vision, the lines on thescreen S will appear'to be stationary. If the receiving antenna systemin the nose of the aircraft is not pointed directly toward the axis ofthe transmitted radio beam, then the pulses received on antenna l andreflector 2 during some lobes or patterns will be of greater magnitudethan others and may approximate the conditions represented in Figs. 3a.and 3b. Where the axis'of the airplane is pointed toward the axis of thetransmitted radio beam, the pulses received on antenna elements I, 2will be of the same magnitude during all four lobes or patterns and thecondition on screen S will be as represented in Fig. 30. Figs. 3a, 3band 30 thus show the position of the aircraft relative to the distantindicating transmitter.

The receiving system of the invention is not limited to a blind landingsystem for aircraft but has general application to a direction findingsystem. For example, a pulse type of transmitter preferably positionedat a high location relative to the earths surface may be arranged tosend out pulses of ultra high frequency energy on an omni-directionalpattern. The receiving system of Fig. 2 can then be used to determinethe direction of the aircraft accommodating the equipment relative tothe remote pulsing transmitter. In this last case, the transmitter canbe located on a high tower or mast, or in a stationary balloon or on avery tall building. This receiver may also be used at a fixed locationto determine the bearing of transmitters whose positions are unknown.

Fig. 2a shows a modification of the system of Fig. 2, in which nointensification pulses are required for the control grid of the cathoderay tube. In both of these figures the same parts are designated by thesame reference characters. The control grid ill of the tube I2 of Fig.2a is now so biased that the electron beam in tube l2 impinges on thescreen S at all times. Grid in can now act as a brilliancy control forthe electron beam. It should be noted that there is no switchingarrangement in Fig. 2a such as is disclosed by the drum of Fig. 2. As aresult, the appearance of the screen S in the tube l2 of Fig. 20. willlook something like Figs. 4a, 4b, and 40 for conditions corresponding toFigs. 3a, 3b and 3c.

The systems of Figs. 2 and 2a may be so designed that the quadraturevoltages applied to the vertical and horizontal deflection plates of thecathode ray tube are different with respect to those hereinbeforeassumed and which result in the showing of Figs. 3a, 3b, 3c and 4a. 4b,40 so that the indication on the screen S corresponds to the position ofaircraft relative to the remote radio transmitter, rather than theposition of the transmitter relative to the aircraft.

Fig. 5 shows a receiving system for use with the invention wherein amore conventional type of cathode ray tube [2' is employed requiring noradial deflecting electrode. In Fig. 5 the two vertical deflectionplates V and the two horizontal deflection plates H are so connected toa. switch 6' that the plates are sequentially supplied with deflectingpotentials. Thus, the vertical plates V are connected to two differentstationary metallic segments 20, 2| on the insulating mountin and thehorizontal plates H connected to two other stationary metallic segments22, 23, as shown. A rotating brush 9' makes successive contacts with thesegments 20, 23, 2| and 22, and this brush is connected through a slipring is to the video output of television type receiver l4 over lead I5.The slip ring is is, of course, insulated from the drive shaft formingpart of the radio frequency line supplying input to the receiver.Rotating joint l3 serves the same purpose as described in connectionwith the systems of Figs. 2 and 2a.

In the operation of Fig. 5, the electron beam in tube l2 strikes thecenter of the screen S in the absence of received incoming pulses. Thegrid l0 acts as va brilliancy control. When pulses are received, theyare applied as video pulses by the receiver output to the deflectionplates of tube l2 in succession through the intermediary of switch 6',and thus the electron beam is deflected first in one direction and thenin another direction. The screen of tube I 2' looks something like Figs.6a, 6b and 60 for conditions corresponding to those of Figs. 3a, 3b and3c or Figs. 4a, 4b and4c. It should be noted that the screen of tube 12'provides a visual indication in the form of a cross whose legs, measuredfrom the center of the screen, indicate the position of the aircraft(accommodating the receiver) relative to the axis of radio beamemanating from remote pulsing radio transmitter. This circuit may bemodified by using a motor driven potentiometer or phase-shiftingtransformer to produce a circular ball-shaped spot of light which movesover the scope in sympathy with direction finder sense.

Although the receiving system of Figs. 2, 2a and 5 have been describedin association with a remote radio pulse transmitter, it should beunderstood that the invention is not limited to the transmission ofpulses but that the receiving system can be used with unmodulated ormodulated continuous waves. A pulse is actually an amplitude modulatedwave varying from minimum amplitude (corresponding to no radiatedcarrier, to maximum amplitude (carrier full on). Although it ispreferred to transmit pulses for blind landing purposes, the use oftransmitted continuous waves is efiective with the receivingsystem ofthe invention for general direction finding purposes. Thus the remoteradio transmitter can send out a sine wave signal modulated by a 1000cycle tone or even by voice, in which case the receiving system isprovided with a switching circuit which selects a section of the voiceor sine wave modulated signal, or for voice other modulation is directlyimpressed on the Oscilloscopes. The carrier radiated by the remotetransmitter is preferably very high frequency above threehundredmegacycles, in order to allow the use of a small and compactantenna at the receiver mounted in an aircraft. The carrier radiatedfrom the remote transmitter may either be amplitude or frequencymodulated, and if frequency modualted then the receiver should have adiscriminator and detector system for supplying a video or audio voltageto the cathode ray demodulated carrier. 'This figure follows generallythe principles of Fig. 2 and the same parts in both of these figures aresimilarly designated. The receiver in Fig. 7 is shown in more detailthan that of Fig. 2. In order to enable the reception of unmodulatedcontinuous waves, there is provided a reactance tube modulator 25 whichcan be connected to the local oscillator through a switch 26 in order tovary the frequency of the local oscillator. The reactance tube modulator25 is connected to a source 21 of audio oscillations; for example, 1000cycles, which is continuously effective on the modulator 25, or thereactance tube may be pulsed. With the switch 26 closed, the receivingsystem then supplies its own modulation in order to receive anunmodulated continuous high frequency radio wave. With the switch 26open, the effective portion of the receiving and indicator system ofFig. '7 is identical with the system of Fig. 2. and is able to receiveinterrupted (pulse) carrier waves, or ordinary amplitude or frequencymodulated continuous carrier waves.

Fig. 8 illustrates a system similar to Fig. '7, except that in Fig. 8there is provided a gating system, sometimes known as a shutter, for usein gating (keying or interrupting) the intermediate frequency stage inthe event it is desired to receive an unmodulated carrier. tem replacesthe local modulation feature of Fig. '7.

' For receiving an unmodulatedradio carrier wave,

the switch 26 is closed and the gate pulse genera- This gating sys-' Itor 28 coupled to the intermediate frequency stage. The pulse generator28 is controlled by a ate pulse oscillator 29 which may be a rectangularpulse oscillator generating audio frequency and video frequencies at arepetition rate of 1000 per second, in which case the intermediatefrequency stage will be gated or interrupted at the rate of 1000 timesper second. With the switch 26' open, the effective portion of thereceiving and indicator system of Fig. '7 is identical with Fig. 2; andis able to receive interrupted (pulse) carrier waves or ordinaryamplitude or frequency modulated continuous carrierwaves. Switch 26' isso arranged in the circuit that it causes the proper bias to be appliedto the intermediate frequency stage in order to enable this stage tofunction properly. When the switch is closed, there is added a positivevoltage to the anode of the tube in the intermediate frequency stage, inaccordance with one form of gating circuit.

Fig. 9 illustrates one form of electronic switch which can be used totake the place of the drum arrangement 6 in any one of the circuits ofFigs. 2, 7 and 8. Fig. 9 illustrates how an intensifier pulse or pulseof positive polarity can be applied to the control grid it of thecathode ray tube l2 for each of four quadrants of the circle traversedby the receiving antenna pattern. This electronic switch includes acontact maker 5i which is driven by a shaft of the motor 3 and rotatesin synchronism therewith. This contact maker is arranged to close a pairof contacts 52 four times during each revolution of the contact maker,as a result of which there will be four pulses of negative polaritysupplied from the negative terminal of a source of unidirectionalpotential -E through the contacts to a trigger circuit 53, 56 for eachrevolution of the contact maker. Or, putting it in other words, duringeach quadrant of the circle traversed by the contact maker there will bea negative pulse supplied to the trigger circuit 53, 5%. This triggercircuit is of the selfrestoring type and comprises a pair of vacuumtubes 53 and 54 whose grid and anode electrodes are interconnectedregeneratively. Normally, vacuum tube 53 is non-conducting, while vacuumtube 54 is conducting. The application of a negative pulse from contacts52 to the cathode of 53 (as shown), and of suflicient magnitude toovercome the negative bias on the vacuum tube 53, will change thetrigger circuit from its normal or steady state (in which tube 53 isnon-conducting and tube 54 conducting) to the active state in which thecurrent passing conditions of-both of these tubes interchange. Thesetubes will stay in the active state for a time period determined by thetime constant of condenser 56 and resistor 55, primarily. After a periodof time, the trigger circuit will restore itself to the steady state.v

Each time the trigger circuit 53, 54 is fired, a pulse of positivepolarity is passed on from the anode of the tube 54 via lead 51 to thecontrol grid ll] of the cathode ray tube l2. This positive pulsesupplied to the control grid I0 is of sufficient magnitude to overcomethe bias on this control grid and enables the electron stream from thecathode of the tube l2 to pass through to the fluorescent screen S ofthe cathode ray tube. It will thus be seen that the circuit of Fig. 9comprises an electronic arrangement for enabling an intensifier pulse tobe applied to the cathode ray tube 12 once for each quadrant of a circleof revolution scanned by the receiving antenna which, in

aeeaoae effect, is equivalent to four intensifier pulses for eachrevolution of the contactor Fig. is an alternative type of electronicswitch which'can take the place of the drum arrangement 6 of Figs. 2, 7and 8, and achieves the same results as Fig. 9. In Fig. 10, power issupplied to the primary winding of transformer 60 whose secondarywinding is connected to the terminals of a phase shifter com-- prisingcondenser 6| and resistor 62. The primary winding of transformer 60 canbe connected to thepower supply of the receiving and indicating systemif this power supply is alternating current, or, alternatively, to onephase of the two-phase generator 5, shown in Figs. 2, 7 and 8. It isassumed that the input to the transformer 60 is of sine wave form whichis synchronized with the rotation of the receiving antenna I, 2. Thatis, if the antenna l. 2 rotates at a speed of 60 revolutions per second,then the power supply to the transformer 60 should be a sine wave of 60cycles per second. It should be noted at this time that if the powersupply from the airplane is employed as an input to the transformer 60,then the motor 3 should be a synchronous motor, whereasif the input tothe transformer 60 is from one phase of the two-phase generator 5, thenthe motor 3 need not be a synchronous motor but should be of fairlyconstant speed. The output from the phase shifter Si, 62 is taken fromthe junction point and supplied to the control grid of a pentode vacuumtube limiter 63.

. This limiter 63 serves to clip off the top and bottom of the sine waveso as to change the incoming wave shape from a sine wave to asubstantially rectangular wave form. The output from the limiter 63 ispassed through a differentiator circuit comprising a condenser 64 and aresistor 65 to the grid of amplifier 66 operating class A. Thedifferentiator passes on to the grid of the amplifier 66 sharp pulsesderived from the slopes corresponding to the starting and trailing edgesof the rectangular wave form pulses in the output of the limiter. Vacuumtube 66 has in its output circuit a transformer 61 which is arranged todifferentiate the output of the amplifier tube so as to produce pulsesof both polarities from each of the pulses applied to the grid of tube66. The secondary winding of the transformer 61 is coupled to thecathode of a selfrestoring type of trigger circuit comprising vacuumtubes 68 and 69. Vacuum tubes 68 and 69 have their grids and anodesinterconnected regeneratively. Normally, tube 68 is non-conducting andtube 69 is conducting in the stable state, and the current passingconditions of these two tubes are reversed in the active state.

The diode III which is located between the secondary winding oftransformer 61 and the trigger circuit 68, 69 assures the application ofonly a negative pulse to the cathode of tube 68'. This negative pulse isof the proper polarity and of suflicient magnitude to trip the trigger68, 69 from the stable to the active state. circuit will restore itselfto normal after a time interval depending upon the time constants of itsassociated circuit elements.

Output from the trigger circuit is obtained from :the anode of tube 69and this output is in the form of positive pulses which are passedthrough differentiator circuit 64', 65 to another amplifier tube 66',also operating class A. The output of the amplifier 66 is passed througha differentiating transformer 61 from which pulses of negative polarityare passed through a diode l0 and This trigger 10 to a self-restoringtrigger circuit 68", 69'. It shouldbe noted that elements 64' to 69'have been given the same reference numerals as 64 to 69 (describedabove) except for the prime designations. This is because-the elementshaving corresponding numbers function similarly.

The output of the trigger circuit 68', 69' is in the form of positivepulses and is passed over lead H to the control grid 10 of the cathoderay tube II. The time constants and adjustments of the circuit elementsof Fig. 10 are so arranged that a positive intensifier pulse is appliedto the control grid ill of tube l2 four times for every cycle of thesine wave constituting the input of the transformer 60.

The operation of the system of Fig. 10 may be better understood from aninspection of the graphs of Fig. 11. Curve I shows the appearance of thesine wave derived from the junction point of the elements 6| and 62 ofthe phase shifter and which is applied to the first grid of the limiter63. Curve 2 shows the appearance of the reshaped wave after it haspassed through the limiter. It should be noted that this wave issubstantially rectangular in wave form. The wave of curve 2 appears onthe anode of the limiter 63 and is applied to the diiferentiator circuit64, 65. Curve 3 shows the pulses which are the results ofdifferentiation by differentiator circuit 64, 65. These pulses arederived from the slopes of the wave form of Fig. 2. Curve 4 showspositive and negative pulses derived in the output of the transformer 61from each of the'diiferentiated pulses of curve 3. Curve 5 shows therectangular wave form pulses derived from the output of the triggercircuit 68, 69. This wave form is obtainpulses of curve 8 are obtainedfrom the anode of tube 69' and constitut the intensifier pulses ofpositive polarity for rendering the cathode ray beam of the tube l2visible.

What is claimed is:

l. A receiving and indicating system for use in determining the positionof a moving vehicle accommodating said system relative to a remote radiotransmitter sending out pulses of radio frequency energy, comprising adirectional receiving antenna arrangement, a motor operating at a slowspeed relative to the repetition rate of the pulses sent out by theremote radio transmitter, a link between said motor and said antennaarrangement for causing the receiving pattern of said antenna to assumedifferent positions of efiectiveness for each revolution of said motor,said different positions corresponding to lobes which would overlap ifthey were produced simultaneously, a superheterodyne receiver coupled tosaid antenna and provided with a detection circuit supplying a videooutput, a cathode ray tube having a cathode, a control electrodenormally biased to prevent the passage of electrons therethrough, a pairof horizontal and a pair of 11 of deflection elements, a connection fromthe output of said detection system to said radial deflection electrode,and a switch operating in synchronism with said motor for supplying saidcontrol electrode with a pulse of positive polarity of suiflcientmagnitude to overcome said bias during each of the different positionsassumed by said antenna receiving pattern for each revolution of saidmotor.

2. For use in a direction finding system wherein a radio transmitterradiates a carrier wave, a receiving and indicating system remotelylocated with respect to said transmitter and mounted in a movingvehicle. said last system including a directional antenna and means forcausing the pattern of said antenna to sequentially and periodicallyassume difierent positions of efiectiveness, a superheterodynemulti-stage receiver coupled to said antenna and provided with a circuitsupplying a video output, a circuit for supplying local audio frequencymodulation to the intermediate frequency stage of said receiver, acathode ray oscilloscope tube having electron deflection elements, and aconnection from said video output to an electron deflection element ofsaid cathode ray oscilloscope.

3. For use in a direction finding system wherein a radio transmitterradiates a carrier wave, a receiving and indicating system remotelylocated with respect to said transmitter and mounted in a movingvehicle, said last system including a directional antenna, and means forcausing the pattern of said antenna to sequentially and periodicallyassume diflerent positions of eflectiveness, a superheterodyne receivercoupled to said antenna and provided with a circuit supplying a videooutput, a reactance tube modulator for varying the frequency of theheterodyning oscillator of said superheterodyne receiver, a cathode rayoscilloscope tube having electron deflection elements, and a connectionfrom said video output to an electron deflection element of said cathoderay oscilloscope.

4. A receiving and indicating system for use in continually determiningthe position of a moving vehicle accommodating said system relative to aremote radio transmitter sending out a radio beam, comprising aunidirectional receiving antenna and means for causing the receivingpattern of said antenna to sequentially and periodically assumedifferent positions of effectiveness corresponding to lobes which wouldintersect if they were produced simultaneously, a superheterodynereceiver coupled to said antenna and provided 'with a detection circuitsupplying a video output, a cathode ray tube having a pair of horizontaland a pair of vertical deflection elements and a radial deflectionelectrode, a circuit for supplying voltages in phase quadrature to saidpairs of deflection elements,

a connection from the output of said detection,

system to said radial deflection electrode, and a gating circuit coupledto said receiver for keying said receiver.

5. A'receiving and indicating system for use in continually determiningthe position of a moving vehicle accommodating said system relative to aremote radio transmitter sending out a radio beam, comprising aunidirectional receiving an-, tenna and means for causing the receivingpattern of said antenna to sequentially and periodically assumedifferent positions of effectiveness corresponding to lobes which wouldintersect if they were produced simultaneously, a superheterodynereceiver coupled to said antenna and provided with a detection circuitsupplying a video output, a cathode ray tube having a pair' to saidintermediate frequency stage under control of a pulse frequencyoscillator.

6. A receiving and indicating system for use in determining the positionof a moving vehicle accommodating said system relative to a remote radiotransmitter sending out a radio beam, comprising a unidirectionalreceiving antenna andmeans for causing the receiving pattern of saidantenna to sequentially and periodically assume different positions ofeflectivness correspondingto lobes which would intersect if they wereproduced simultaneously, a superheterodyne receiver coupled to saidantenna and provided witha detection circuit supplying a video output, acircuit for modulating the energy passing through: said receiver at anaudio frequency rate, a switch between said last circuit and saidreceiver, a cath-t ode ray tube having electron deflection electrodes,-and a connection from the output of said detection system to at leastone of said deflection electrodes.

7. A receiving and indicating system for use in determining the positionof a moving vehicle accommodating said system relative to a remote radiotransmitter sending out a radio beam, comprising a unidirectionalreceiving antenna and means for causing the receiving pattern of saidantenna to sequentially and periodically assume different positions ofeffectiveness corresponding to lobes which would intersect if they. wereproduced simultaneously, a superheterodyne receiver coupled to saidantenna and provided with a detection circuit supplying a video output,a cathode ray tube having a pair of horizontal and a pair of verticaldeflection elements and a radial deflection electrode, a circuit forsupplying voltages in phase quadrature to said pairs of deflectionelements, a connection from the output of said detection system to saidradial deflection electrode, a circuit coupled to said receiver formodulating the energy passing through said receiver, and a switchfordisconnecting said last circuit from said receiver.

8. For use in a direction finding system wherein a radio transmitterradiates a radio frequency carrier wave, a receiving and indicatingsystem remotely located with respect to said transmitter and mounted ina moving vehicle,-said last system including a directional antennalocated in the front of said vehicle and means for causing the patternof said antenna to sequentially and periodically assume differentpositions of efiectiveness, said difierent positions corresponding tolobes which would overlap at points of substantially greatest slope ifthey were produced simul taneously, a television type of superheterodynereceiver coupled to said antenna and provided with a wide bandintermediate frequency stage, a wide band detector stage, an automaticgain control circuit and a video detector circuit having a band withconsiderably narrower than the band width of the preceding stages of thereceiver, a cathode ray oscilloscope tube having electron deflectionelements, and a connection from the output of said video detectorcircuit awroaa 13 to an electron deflection element of said cathode rayoscilloscope.

9. A system in accordance with claim 1, char acterlzed in this, thatsaid switch is an electronic type of switch including a self-restoringtrigger circuit.

- 10. A receiving and indicating system for use in determining theposition of a moving vehicle accommodating said system relative to aremote radio transmitter sending out pulses of radio frequency energy,comprising a directional receiving antenna arrangement, a motoroperating at a slow speed relative to the repetition rate of the pulsessent out by the remote radio transmitter, a link between said motor andsaid antenna arrangement for causing the receiving pattern of saidantenna to assume dlfierent positions of effectiveness for eachrevolution of said motor, said diflerent positions corresponding tolobes which would overlap if they were produced simultaneously, asuperheterodyne receiver coupled to said antenna and provided with adetection circuit supplying a video output, a cathode ray tube having acathode, a control electrode normally biased to prevent the passage ofelectrons therethrough, and electron deflection electrodes, a connectionfrom the output of said detection system to one of said deflectionelectrodes, and a switch operating in synchronism with said motor forsupplying said control electrode with 14 pulses of positivepolarlty orsufllcient magnitude to overcome said bias during said diiferent lobepositions.

WILLIAM A. MILLER.

REFERENCES crmn The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,130,913 Tolson Sept. 20, 19382,151,549 Becker Mar. 21, 1939 2,151,917 Hyland Mar. 28, 1939 2,189,549Hershber'ger Feb. 6, 1940 2,202,400 Roberts Mali '28, 1940 2,263,377Busignies et al Nov. 18, 1941 2,295,412 Little Sept. 3, 1942 2,334,247Busignies Nov. 16, 1943 2,380,929 Ahier et a1. Aug. 7, 1945 2,388,262Ganiayre et al Nov. 6, 1945 2,405,930 Goldberg et al Aug. 13, 19462,407,281 Johnson et a1 Sept. 10, 1946 2,408,041 Busignies Sept. 24,1946 2,412,612 Godet Dec. 17, 1946 2,412,702 Wolff Dec. 17, 19462,412,703 Wolfi Dec. 17, 1946 2,418,846 Meacham Apr. 15, 1947 2,419,219Johnstone Apr. 22, 1947 2,447,502 Hardy Aug. 24, 1948

